Blood viscosity is a physical value that assays flow resistance of the blood in a blood vessel, and specifically, can be divided into a whole blood viscosity and a plasma viscosity. An abnormal increase in the blood viscosity causes an increase in a shear stress and the flow resistance acting on an inner wall of the blood vessel, thereby, significantly increasing a risk of developing acute cardiovascular disease and microvascular disease. In addition, the plasma viscosity is used to diagnose inflammation in the body and is one of main causes increasing the whole blood viscosity.
The whole blood viscosity shows flow characteristics in which viscosity continuously changes depending on a systolic phase and a diastolic phase of the heart because the viscosity decreases when blood flows at a high speed (when a shear rate is high) and the viscosity increases when blood flows at a low speed (when the shear rate is low) due to complex effects of red blood cells and plasma proteins in whole blood. Fluids with such flow characteristics are called non-Newtonian fluid and it is necessary to accurately measure the whole blood viscosity for a total shear rate (for example, 1 to 1,000 s-1) so as to accurately grasp the non-Newtonian flow characteristics of the blood.
The plasma viscosity measured by using plasma obtained by separating the red blood cells from the whole blood, does not vary with the shear rate and is constant unlike the whole blood viscosity. Fluid with such flow characteristics is called Newtonian fluid.
Presently, the blood viscosity is measured by a precisely devised large equipment once a blood sample obtained and transmitted to the measurement room. It is impossible to measure the blood viscosity at a desired place and time due to an absence of a measurement technique capable of performing an on-site and real time inspection proposed in the present patent. Previously, the viscosity of blood was measured by using the following methods.
First, a U-shaped double-vertical-tube/single-capillary viscometer measures viscosity by measuring a difference in height, which is reduced by gravity, by providing a height difference between blood contained in the two vertical capillary tubes, and has the following advantages.
The U-shaped double-vertical-tube/single-capillary viscometer uses a disposable U-shaped tube, because it is easy to use in clinical applications since there is no need to clean, no risk of infection, capable of viscosity measurement for 1 to 1000 s{circumflex over ( )}-1 shear rate range, and can measure both the whole blood viscosity and the plasma viscosity can be measured.
However, there are problems where the U-shaped double-vertical-tube/single-capillary viscometer causes an error in viscosity measurement in the low shear rate range less than 1 s{circumflex over ( )}-1 due to a structural constraint, hardly measures a viscosity value lower than or equal to 1 cP due to characteristics of a measurement algorithm, requires a large amount of whole blood of 3 mL or more in order to measure the whole blood viscosity, and requires a lot of whole blood of 6 mL or more so as to measure the plasma viscosity after plasma is separated from the whole blood. In addition, there are problems in which a separate dyeing process is required for measuring the plasma viscosity, and it is difficult to perform point-of-care testing due to inconvenient transport caused by a large size and a heavy weight because a fixed type method is used.
The Brookfield viscometer measures viscosity by measuring a torque acting on a plate due to fluid while rotating the fluid put in a chamber in a state where a spring is connected to the plate, has the following advantages. The Brookfield viscometer is capable of performing the measurement using a small amount of blood of approximately 0.5 mL, and can measure both the whole blood viscosity and the plasma viscosity. However, since the Brookfield viscometer measures viscosity only for a specific shear rate, it is practically impossible to measure the whole blood viscosity with respect to the total shear rate in case of the whole blood viscosity, and because the Brookfield viscometer does not have a disposable measurement structure, once the measurement is performed, a measurer has to clean the viscometer to remove blood by hand for the next measurement, and furthermore there is a risk of infection caused by blood during the cleaning process, it is difficult to use the viscometer. In addition, it is difficult to perform point-of-care testing due to inconvenient transport caused by a large size and a heavy weight because a fixed type method is used.
The Ostwald glass capillary plasma viscometer measures viscosity by measuring time when plasma of 10 mL passing through a vertical glass tube including a capillary tube and has an advantage of not using any electronic device and can be used at any location. However, in order to obtain plasma of 10 mL required for measuring the plasma viscosity, a large amount of whole blood of 20 mL is required, the whole blood viscosity cannot be measured, remeasurement is performed after the capillary tube is cleaned once the measurement is performed, and since a diameter of the capillary tube is less than 1 mm, it is impossible to clean the capillary tube realistically. In addition, the Ostwald glass capillary plasma viscometer is exposed to the risk of infection caused by the blood during the cleaning process, and thus, the viscometer cannot be used in the clinic, and since the measurer directly measures a height change time using a stopwatch, there is a problem that a large error occurs depending on the measurer.